The present invention concerns a magnetic coating-thickness gauge of small size, resembling a pencil.
In such known coating-thickness gauges as are suitable for use with one hand, the holding magnet or permanent magnet is situated at the lower end of a rod that is connected at its upper end to the opposite end of the housing via a measuring spring. In these known coating-thickness gauges, as a rule the holding magnet with its hemispherically-shaped dome projects from an opening at the lower end of the housing and with the latter is placed on the surface coating to be measured. For the measurement of the thickness of the surface coating of the ferromagnetic support material, the tubular or cartridge-shaped housing of the measuring device is moved upward against the measuring surface or is pulled away from it with the right or left hand until the force of the measuring spring supporting the holding magnet exceeds the holding force of the permanent magnet and the latter is thus abruptly lifted from the measuring surface.
On the rod to which the permanent magnet is attached there is a marking that on lifting of the housing, which is constructed of transparent plastic or is provided with a slit opening moves along the measuring scale, and in order to establish the measured coating thickness, the movement of this marking with respect to the measuring scale must be observed exactly in order to read the position of the marking on the measuring scale as accurately as possible at the moment of separation of the holding magnet from the measuring surface. However, this is associated with great difficulties, for the measuring device with the measuring dome of the holding magnet definitely cannot always be placed on the measuring surface in a constant perpendicular position. However, due to an oblique positioning, the holding force of the magnet on the coating changes, and also the measuring dome is easily unintentionally drawn along the measuring surface, so that from this alone erroneous measurements results. In addition, the particular value measured cannot be stored on the instrument.
Aside from the fact that in kmown measuring devices the exposed measuring dome of the holding magnet can be easily damaged, in these, according to whether measurements are made on measuring surfaces that are horizontal, inclined, or overhead, the addition weight of the support rod for the holding magnet enters into the results of the measurements in such a way as to falsify the measurements read off.
In known coating-thickness gauges with a pencil-shaped housing there is thus not only the varying positioning of the devices on the coating to be measured entailing varying measurements, but it is also extremely difficult to read the position of the mark on the measurement scale exactly at the moment of the sudden separation of the holding magnet from the measuring surface.